1. Field of the Invention
This invention relates to the coating of the surface of a refractory transparent substrate material, such as a glass sheet, with a semi-reflective adherent film of tin oxide by projecting a pyrolytically decomposable tin compound against substrate material.
2. Prior Art
It is well known that a thin adherent film of tin oxide disposed on the surface of a refractory transparent material such as a glass sheet or a vitreous ceramic material, will impart heat protective properties to the substrate material by substantially increasing the amount of infra-red radiation reflected from the coated surface while maintaining a satisfactory radiation transmission coefficient in the visible range of the solar spectrum.
It has heretofore been suggested that such infra-red reflective and visible spectrum transmissive films or coatings of tin oxide be formed in situ on the surface of the refractory substrate material by heating the substrate material to a high temperature but nonetheless below the softening point of said material and then projecting onto the surface of the hot substrate material an organic or inorganic tin compound that decomposes by pyrolysis upon contact with the surface of the hot substrate material, thereby leaving on said surface a heat-reflective transparent adherent film of tin oxide.
Up to now, this procedure has been carried out by various processes which, in general, involve the projection of a solution of a tin compound in an aqueous or organic solvent onto the surface of the refractory substrate material to be coated. However, these prior processes have not been entirely satisfactory because they all have drawbacks, either as far as the quality of the tin oxide film obtained is concerned (for example, unsatisfactory adherence, uniformity of thickness, transparency, optical or electrical conductivity properties, and the like), or as regards difficulties or complications involved in actual application (for example, preparation of the surface to be coated, auxiliary chemical reagents, preparation of solutions to be sprayed, removal of excess solution and solvent vapors or decomposition products, and the like).